Download the moebuntu sound theme file (Moesound_iori.tar.gz) from here, and expand it.
Put the sound theme into "/usr/share/sounds."
You can access files/folders as an administrator by typing this command into the Terminal.
$ sudo nautilus /usr/share/sounds
[for Ubuntu 14.04 LTS/14.10]
After you put it in the folder, launch "Ubuntu Tweak" and go to "Tweaks" and click on "Sound",
and change the settings as below. (e.g. sound theme: Moesound_iori)
Sound theme:Moesound_iori
[for Ubuntu 15.04/15.10]
Go to "/usr/share/sounds", and then change the name of the folder from "Moesound_ior" to "ubuntu".
[for Ubuntu 16.04 LTS - 17.04]
1) Install "dconf-editor" via "Ubuntu Software".
2) Open "dconf-editor" and move to the left pane of the "dconf-editor" > "org" > "gnome" > "desktopr" > "sound".
3)In this "theme name" section, change the "file name from "ubuntu" to "Moesound_iori".
By default, Ubuntu Startup sound is disabled.
Change this setting to be enabled.
Open "Dash" > "Startup Applications...",
Click "Add" and input the settings below.
Name: [GNOME Login Sound]
Command: [/usr/bin/canberra-gtk-play --id="desktop-login" --description="GNOME Login"]
Comment: [Plays a sound whenever you log in]
Up to here, you have completed the Moe Sound theme settings. Logout and check the result.